The present invention relates generally to electrical power systems, and particularly to systems for limiting peak electrical power drawn by mining excavators from an electrical power source.
Many applications depend on electricity supplied by an electrical power distribution network, such as the electrical power grid operated by an electrical power utility company. Some commercial and industrial applications draw significant power. Loads are often dynamic, and peak power demand may approach, and, in some instances, exceed, the maximum power available from the electrical power distribution network. Excessive peak power demand may lead to voltage sags and temporary outages in the electrical power distribution network. Therefore, not only may the performance and reliability of the application of interest be degraded, but also service to other customers of the electrical power utility company may be disrupted.
One application which draws significant electrical power is mining. In a mining operation, the electrical power distribution network feeds a wide spectrum of loads, ranging from small industrial motors to large draglines. Electrical mining excavators, such as electric shovels and draglines, present a cyclic load to the electrical power distribution network. Although the average power drawn by these machines may be about 55% of their peak power demand, in some instances, the peak power demand may approach the generation limits at the individual feeders providing input power to the machines. For example, an electric shovel may draw peak powers on the order of 3.5 megawatts, and a dragline may draw peak powers on the order of 24 megawatts.
In addition to improved performance and reliability, there is also an economic incentive for reducing peak power demand. Electrical power utility companies supplying power to the mines typically measure the power demand of a mine based on 15-minute intervals, and billing is adjusted for peak power demand during each 15-minute interval. What are needed are method and apparatus for limiting peak power drawn by mining excavators from an electrical power distribution network. Method and apparatus which reduce wasted energy are particularly advantageous.